The invention relates to breathing systems in the form of single hose, two stage SCUBA regulators in general and more specifically to such regulators employing a pneumatic assist in the second stage thereof so that the regulator acts in close response to user demand and, equally importantly, has generally equivalent response parameters over a very wide range of ambient pressures and breathing gas supply pressures.
The well-known art term SCUBA is an acronym for a self contained underwater breathing apparatus and a scuba regulator is a device that supplies breathing gas to a user from a source of breathing gas under elevated pressure. Modern day scuba regulators are demand two stage, single hose regulators and include a first stage, an intermediate pressure hose and a second stage which delivers gas at ambient pressure to the diver. Typically, the first stage is attached to a tank of air or other gas under pressure of from generally 2500 psi to 4000 psi when full. The first stage reduces tank pressure to an intermediate pressure of 100 to 150 psi over ambient pressure and delivers the gas to an intermediate pressure hose. This hose is in turn connected to a second stage having an outlet with a mouthpiece for the diver. The second stage delivers air to the diver on demand at ambient pressure. An exhaust port having a one way flapper valve vents exhaled air into the water. Prior art single hose regulator second stages are typically quite simple and include a chamber having a downstream valve with a spring loaded lever arm resting against an inhalation diaphragm, a mouthpiece, and a one way flapper valve for venting exhaust. Upon inhalation, the inhalation diaphragm flexes inwardly in response to the pressure drop in the chamber created by user demand. The flexing diaphragm moves the lever to open the downstream valve to admit air from the intermediate pressure hose to the chamber and thus the diver through the mouthpiece. Upon cessation of demand by the user and/or exhalation by the diver through the mouthpiece, the inhalation diaphragm moves outwardly, allowing the lever arm to return to a normal rest position whereupon the downstream valve closes to terminate delivery of intermediate pressure air to the second stage chamber.
In a perfectly designed system, demand response of the mechanical breathing apparatus would precisely correspond to user demand on both the inhalation and exhalation phases of a breathing cycle and, additionally, a sufficient flow rate would be provided to the diver-user regardless of demand or ambient pressures. Of course, this does not happen but the principal intent of all designs is to deliver air in sufficient quantities to the diver regardless of ambient pressures and with minimum inhalation and exhalation resistance. Accordingly, optimum sensitivity of the breathing system to user demand coupled with flow capacities that will meet diver demand under normal and elevated requirements (e.g., hyperventilation) are essential criteria in the designing of an adequate SCUBA regulator.
In the present invention, breathing system sensitivity to user demand is greatly enhanced by provision of a pilot valve actuating assembly, which assists in the opening and closing of the valve delivering air to the second stage chamber. The use of pilot valve assists in breathing systems to amplify response of supply valves is, of course, not new. For example, U.S. Pat. No. 2,597,039 issued to H. Seeler on May 20, 1952 discloses a pressure breathing demand oxygen regulator particularly designed as the essential component of an aviator's high altitude mask and incorporating a control chamber having a main oxygen supply valve therein together with a pilot valve, lever linked to the inhalation diaphragm of the breathing system. Upon user demand, the lever is depressed thereby opening the pilot valve which vents control chamber pressure downstream to the user. This creates a pressure drop in the chamber which thus causes the main supply valve to open and supply oxygen to the user. A bleed line is communicated from source pressure to the control chamber so that upon cessation of user demand, the pilot valve closes; source and control chamber pressure are then equalized through the bleed line.
A similar design for an aviator's mask is disclosed in two patents assigned to the Robertshaw - Fulton Controls Company of Richmon, Virginia, these being U.S. Pat. Nos. 2,988,085 issued to L. Jones on June 15, 1961 and 3,076,454 issued to J. R. Evans et al on Feb. 5, 1963. This design also incorporates a surge chamber communicated to the main valve of the system to reduce chattering or vibration of the main valve. Typically, such chattering is an annoying problem in such designs incorporating a diaphragm valve as the main valve for supplying fluid from source to user.
The only pilot valve regulator designed for SCUBA system use known to applicant is disclosed in U.S. Pat. No. 3,783,891 issued to R. A. Christianson on Jan. 8, 1974 and assigned to Under Sea Industries of Compton, California. This system incorporates a sliding piston valve instead of a diaphragm valve as the main supply valve of the regulator second stage, the piston having a central hose communicated with a control chamber closed by an upstream pilot valve which is linked to the inhalation diaphragm of the regulator second stage. The instantly disclosed and claimed design incorporates radical departures from the Christianson patent, principally by providing a main diaphragm valve rather than a piston valve and an upstream pilot valve rather than a downstream pilot valve.